This invention relates generally to electrically controlled unit injectors and more specifically to the means for venting or dumping the fuel from such an injector having a variable volume timing and metering chamber located therein. A single solenoid unit injector is shown in U.S. Pat. No. 4,281,792 by Sisson et al which illustrates a unit injector capable of independently controlling the timing and metering functions by a single solenoid. A single dump unit injector employing a three-way control valve is described by Sisson in his Application Ser. No. 364,813. In my Patent Application Ser. No. 364,723, I disclose a unit injector having a dump port to relieve the pressure in the timing chamber and another dump port to relieve the pressure in the metering chamber. To enhance the closing of the nozzle portion of the injector, the pressurized fluid in the metering chamber was dumped via a spring cage to a source of fuel via a restricting upstream orifice. While this invention generates enhanced forces to close the nozzle, it does not provide for the unrestricted dumping of fuel from the metering chamber. The Patent Application Ser. No. 364,813 shows a unit injector having a single dumping port which directly relieves the pressure within the timing chamber and indirectly relieves the pressure in the metering chamber. This injector uses a check valve between the metering chamber and the nozzle which is subject to high pressure surges. In contrast, the present invention defines a unit injector having a unique structural configuration wherein the timing chamber dump port is connected to the fuel return of drain via the nozzle spring cage and a flow restricting orifice. In addition the metering chamber is dumped in a relatively unrestricted manner to either the source or to drain. The present invention offers the advantage of enhanced and rapid nozzle closure upon fuel dumping by routing the pressurized timing chamber fuel to the spring cage to force the nozzle closed while permitting unrestricted dumping of the fuel in the metering chamber. The high level of spring cage pressure during and after nozzle closure, combined with the rapid loss of pressure in the metering chamber tends to hold the nozzle closed, thereby reducing or eliminating secondary injections. In addition, the present invention reduces or eliminates the blow back of combustion gases through the injector because of its fast nozzle closure and its tendency to hold the nozzle closed immediately after injection.
Accordingly, the present invention comprises:
A cam driven fuel injector having a fuel inlet port adapted to be connected to a supply or source of fuel and having a drain port; including a body defining a bore having a driven or pumping piston reciprocatively situated therein, a metering or floating piston reciprocatively positioned within said bore remote from the pumping piston; a timing chamber and a metering chamber defined in the bore and metering and timing chamber dump ports located thereon; a spring cage located remote from said cylinder, a spring normally tending to bias a needle valve in a closed position to close off an outflow orifice; a plurality of fuel carrying passages for communicating fuel to the metering and timing chambers and from the timing chamber dump port to the spring cage and needle valve; a single electrically operated control valve for controlling fuel flow to said timing and metering chambers; and a spring cage dumping passage communicated between the spring cage and the return port housing, in series, a flow restricting orifice and a check valve and wherein the metering chamber dump port is communicated directly to the source of fuel.